Thesis for the degree of Licentiate of Technology Sundsvall 2011 High Speed (MHz) Switch Mode Power Supplies (SMPS) using Coreless PCB Transformer Technology Kotte Hari Babu Supervisors: Associate Professor Kent Bertilsson Professor Bengt Oelmann Electronics Design Division, in the Department of Information Technology and Media Mid Sweden University, SE-851 70 Sundsvall, Sweden ISSN 1652-8948 Mid Sweden University Licentiate Thesis 62 ISBN 978-91-86694-41-8 Akademisk avhandling som med tillstånd av Mittuniversitetet i Sundsvall framläggs till offentlig granskning för avläggande av licentiatexamen i elektronik fredagen den 27 May 2011, klockan 10:00 i sal M102, Mittuniversitetet Sundsvall. Seminariet kommer att hållas på engelska. High Speed (MHz) Switch Mode Power Supplies (SMPS) using Coreless PCB Transformer Technology Kotte Hari Babu © Kotte Hari Babu, Electronics Design Division, in the Department of Information Technology and Media Mid Sweden University, SE-851 70 Sundsvall Sweden Telephone: +46 (0)60 148982 Printed by Kopieringen Mittuniversitetet, Sundsvall, Sweden, 2011 Dedicated to the divine lotus feet of Bhagawan Sree Satya Sai Baba & Sree Sadguru Krishnendra Santani ‘HELP EVER, HURT NEVER’ iii iv ABSTRACT The most essential unit required for all the electronic devices is the Power Supply Unit (PSU). The main objective of power supply designers is to reduce the size, cost and weight, and to increase the power density of the converter. There is also a requirement to have a lower loss in the circuit and hence in the improvement of energy efficiency of the converter circuit. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. At present the switching frequency of the converter circuit is limited due to the increased switching losses in the existing semiconductor devices and in the magnetic area, because of increased hysteresis and eddy current loss in the core based transformer. Based on continuous efforts to improve the new semi conductor materials such as GaN/SiC and with recently developed high frequency multi-layered coreless PCB step down power transformers, it is now feasible to design ultra-low profile, high power density isolated DC/DC and AC/DC power converters. This thesis is focussed on the design, analysis and evaluation of the converters operating in the MHz frequency region with the latest semi conductor devices and multi-layered coreless PCB step-down power and signal transformers. An isolated flyback DC-DC converter operated in the MHz frequency with multi-layered coreless PCB step down 2:1 power transformer has been designed and evaluated. Soft switching techniques have been incorporated in order to reduce the switching loss of the circuit. The flyback converter has been successfully tested up to a power level of 10W, in the switching frequency range of 2.7-4 MHz. The energy efficiency of the quasi resonant flyback converter was found to be in the range of 72-84% under zero voltage switching conditions (ZVS). The output voltage of the converter was regulated by implementing the constant off-time frequency modulation technique. Because of the theoretical limitations of the Si material MOSFETs, new materials such as GaN and SiC are being introduced into the market and these are showing promising results in the converter circuits as described in this thesis. Comparative parameters of the semi conductor materials such as the v energy band gap, field strengths and figure of merit have been discussed. In this case, the comparison of an existing Si MOSFET with that of a GaN MOSFET has been evaluated using a multi-layered coreless PCB step-down power transformer for the given input/output specifications of the flyback converter circuit. It has been determined that the energy efficiency of the 45 to 15V regulated converter using GaN was improved by 8-10% compared to the converter using the Si MOSFET due to the gate drive power consumption, lower conduction losses and improved rise/fall times of the switch. For some of the AC/DC and DC/DC applications such as laptop adapters, set- top-box, and telecom applications, high voltage power MOSFETs used in converter circuits possess higher gate charges as compared to that of the low voltage rating MOSFETs. In addition, by operating them at higher switching frequencies, the gate drive power consumption, which is a function of frequency, increases. The switching speeds are also reduced due to the increased capacitance. In order to minimize this gate drive power consumption and to increase the frequency of the converter, a cascode flyback converter was built up using a multi-layered coreless PCB transformer and this was then evaluated. Both simulation and experimental results have shown that with the assistance of the cascode flyback converter the switching speeds of the converter were increased including the significant improvement in the energy efficiency compared to that of the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the power converter, double ended topologies were chosen. For this purpose, a gate drive circuitry utilising the multi-layered coreless PCB gate drive transformer was designed and evaluated in both a Half-bridge and a Series resonant converter. It was found that the gate drive power consumption using this transformer was less than 0.8W for the frequency range of 1.5-3.5MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the series resonant converter was found to be 86.5% with an output power of 36.5W. vi SAMMANDRAG Den viktigaste delen i alla elektroniska apparater är strömförsörjningsenheten och idag sker en konstant utveckling att minska storlek, kostnad och vikt, och att öka effekttätheten för dessa. Det finns också ett krav att minska förlusten i omvandlaren och därmed öka verkningsgraden. Vid högre switchfrekvens minskar storleken på de passiva komponenter såsom transformatorer, induktorer och kondensatorer, vilket resulterar i en kompakt storlek, vikt och ökad effekttäthet i omvandlaren. För närvarande är switchfrekvensen begränsad av förluster i befintliga halvledarkomponenter men även i magnetiska komponenter, på grund av ökad hysteres- och virvel-strömmar i kärnbaserade transformatorer. Nylig utveckling inom komponenter i kiselkarbid och galliumnitrid tillsammans med utvecklade kärnfria transformatorer möjliggör kompakt design med mycket låg bygghöjd av isolerade AC/DC och DC/DC omvandlare. Denna avhandling fokuserar på design, analys och utvärdering av omvandlare är MHz frekvenser konstruerade med de senaste halvledarkomponenter och flerlagers kärnfria kretskortstransformatorer. En högfrekvent isolerad flyback DC-DC-omvandlare baserade på kärnfri 2:1 kretskortstransformator har konstruerats och utvärderats. Mjukswitchade tekniker har införts i syfte att minska förluster i kretsen. Flybackomvandlaren har verifierats upp till ca 10W, i frekvensområdet 2.7-4 MHz. Verkningsgraden hos den kvasiresonanta flyback omvandlare är 72-84% under nollspänningsswitchning (ZVS). Utspänningen från omvandlaren reglerades genom modulation med konstant frånslagstid. På grund av de teoretiska begränsningarna i kisel MOSFETs, visar nya komponenter i GaN lovande resultat i omvandlarkretsar i denna avhandling. I en jämförelse mellan en befintlig kisel och en GaN MOSFET i en högfrekvent isolerad 45 till 15V återkopplad omvandlare visade GaN 8-10% högre verkningsgrad. Förbättringar kan härledas framför allt lägre ledningsförluster, snabbare till och frånslag samt lägre effektkonsumption för gatedrivningen vii För högfrekventa omvandlare vid höga spänningar ökar förlusterna i gatedrivningen både p.g.a. frekvensen men även spänningsnivån. En cascode omvandlare har designats och utvärderas vilken kräver en mycket lägre gatedrivning då Millereffekten elimineras. Både simuleringar och experimentella resultat har visat att denna design kunnat öka prestandan jämfört med en traditionell design. För att maximera utnyttjandegraden av transformatorn, och minska spänningsnivån på transistorerna har en högfrekvent halv-brygga dessutom implementerats och utvärderats. En flytande gatedrivare som arbetar upp till 350V i MHz området har därför också utvecklats som bygger på en mindre kretskortstransformator. Effektförbrukningen för gatedrivningen av båda transistorer har verifierats till att vara mindre än 0.8W i frekvensområdet mellan 1.5-3.5MHz. Den realiserade halvbryggan har karakteriserats i en serie- resonant konfiguration till att kunna ge upp till 86.5% verkningsgrad med en uteffekt av 36.5W. viii ACKNOWLEDGMENT I would like to show my great appreciation of my supervisors Associate Professor Kent Bertilsson and Prof. Bengt Oelmann for their guidance and for giving me the opportunity to pursue my licentiate studies at Mid Sweden University, Sundsvall, Sweden. I am very grateful to Radhika Ambatipudi for her kind support during my studies. Thanks to my colleague and friend Muhammed Anzar Alam who has shared many memorable moments with me during this period. I am also grateful to Fanny Burman, Lotta Söderström, Christine Grafström, Krister Alden, Benny Thörnberg, Magnus Engholm, Claes Mattsson, Kannan Thiagarajan, Cheng Peng, Najeem Lawal, Sebastian Bader, Abdul Majid, Jawad Saleem, Stefan Haller, Mazhar Hussain,